176 



Sir J. C. Bose and Mr. S. C. Guha. 



effector when the right half of the lamina is alone stimulated, is indicated by 

 galvanometric negativity ; for concordant movement under the above con- 

 dition, the impulse which actuates the left effector should be of opposite 

 sign, i.e., of galvanometric positivity. 



I carried out two sets of experiments on the above lines with an identical 

 leaf of Helianthus. First, I carried out the usual experiment of the electric 

 ■detection of transmitted excitatory impulse. In this, one of the contacts 

 was made with the right nerve in the petiole, the second being with a distant 

 indifferent point. The nerve endings on the right half of the lamina were 

 electrically stimulated and the transmitted impulse along the nerve gave the 

 usual excitatory reaction of galvanometric negativity. A second pair of 

 contacts were made for detection of transmitted impulse in the nerve of the 

 left flank of the petiole. Stimulation of the nerve termination of the right 

 half of the lamina gave in the left nerve a reaction of galvanometric positivity. 

 In practice stimulus was always applied to the right half of the lamina, and 

 galvanometric connections were made alternately with the right and left 

 nerve. The results were always the same and showed that excitation of a 

 nerve gave rise to an opposite reaction in the contiguous nerve. There is no 

 doubt that these two nervous impulses of opposite signs reaching the 

 antagonistic tissues of the two flanks of the motor organ must be of import- 

 ance in the co-ordination of the resulting movements. 



General Summary. 



In certain leaves the helio tropic adjustment is brought about by trans- 

 mission of nervous impulse to the motor organ. A continuity is shown to 

 exist in the response of " sensitive " and ordinary plants. Mimosa pudica 

 is taken as a type of the former, and Helianthus annum of the latter. 

 Mechanical response is brought about in both by the differential excitability 

 of the upper and lower halves of the motile organ. The lower half in both is 

 the more excitable. Local stimulation of the abaxial half of the organ induces 

 an erectile movement, that of adaxial half a more rapid downward movement. 



Heliotropic curvature of a stem is due to the joint effects of contractile 

 reaction of tiie proximal and expansion of the distal side. 



The daily periodic movements of the leaves of Mimosa and of Helianthus 

 are essentially similar. The diurnal movement is brought about by the 

 variation of the geotropic action with changing temperature, and by the 

 varying intensity of light. The leaves erect themselves during the fall of 

 temperature from thermal noon at 2 p.m. to about 5.30 p.m. Owing to the 

 rapid diminution of light in the evening the leaves undergo an abrupt fall 



